Latent tuberculous infection in household contacts of multidrug-resistant and newly diagnosed tuberculosis.

BACKGROUND: Differences in the prevalence of latent tuberculous infection (LTBI) and tuberculosis (TB) disease among contacts of patients with multidrug-resistant TB (MDR-TB) and drug-susceptible TB are not well understood. OBJECTIVE: To compare the prevalence of tuberculin skin test (TST) positivity in household contacts of patients with MDR-TB and in contacts of patients never previously treated for TB ('new TB'). DESIGN: Consecutive patients with MDR-TB and their household contacts at nine urban district clinics in Viet Nam were screened for TB and LTBI, and followed up for 6 months. LTBI was defined as a TST result of at least 10 mm. RESULTS: A total of 167 patients with TB and their 337 household contacts were recruited. A total of 167/180 (25.8%) contacts of new TB patients and 60/147 (40.8%) contacts of MDR-TB patients were TST-positive (odds ratio [OR] 2.0, 95%CI 1.3-3.2). Contacts of MDR-TB patients were more likely to have baseline chest radiograph findings consistent with TB (OR 2.6, 95%CI 1.4-5.0). CONCLUSION: Contacts of MDR-TB patients have a high risk of developing TB. Measures to reduce Mycobacterium tuberculosis transmission and accelerate the detection of disease among high-risk contacts should be prioritised to curb the MDR-TB epidemic.